1. Field of the Invention
The present invention relates to a machine tool, and particularly to, a machine tool comprising a tool-driving unit which is liftable relative to a support column and which includes a lift frame movable up and down along a pair of left and right guide rails on a front surface of the column to extend vertically thereon, and a tilting-type turret head supported on a front surface of the lift frame for rotation about an axis inclined with respect to the front and rear direction of the frame in a horizontal plane.
2. Description of the Prior Art
A machine tool with a tool-replacing turret is known from Japanese patent publication No. 32112/72 and Japanese patent application laid-open No. 122976/77. There is also known a machine tool comprising a supporting device for a tool-driving unit liftable relative to a support column, such as shown in FIG. 15, the tool-driving unit including a lift frame movable up and down along a pair of left and right guide rails laid on a front surface of the column to extend vertically thereon, and a tilting-type turret head supported on a front surface of the lift frame for rotation about an axis inclined with respect to the front and rear direction.
Referring to FIG. 15, the pair of left and right guide rails 291 and 292 are mounted on the front surface of the column 290 of the machine tool to extend vertically thereon, so that the lift frame 293 of the tool driving unit A' may be moved up and down along the guide rails 291 and 292 while receiving a vertically moving force from a vertical feed screw 294. The tilting-type turret head 296 rotatable about an axis extending inclined to the front and rear direction of the frame 293 on a horizontal plane is supported at a leading end of a cylindrical support 295 formed on a front portion of the lift frame 293 and has a cylindrical connection 297 whose outer periphery is rotatably supported through a bearing 298 on an inner peripheral surface of the cylindrical support 295 of the lift frame 293. An outer peripheral flange 293f at the outer end of the cylindrical support 295 and an outer peripheral flange 296f at the connection of the turret head 296 are slidable on each other and have tapered surfaces on their back surfaces. An annular clamp 299 is fitted over the outer peripheral surfaces of the outer peripheral flanges 293f and 296f for inhibiting the rotation of the turret head 296 relative to the lift frame 293 as required.
A gear 200 is integrally secured to an end face of the cylindrical connection 297 of the turret head 296 and is in mesh with a gear 205 which is driven through a bevel gear 202, a bevel gear 203 and a gear shaft 204 by a turret-rotating motor 201 disposed on the lift frame 293.
A rotational driving force from a tool-rotating motor 206 disposed on the lift frame 293 is transmitted through a coupling 207 connected to an output shaft of the tool-rotating motor 206, gears 208, 209 and 210, a spline 211 on a gear shaft of the gear 210, and a driving engage member 213 of a clutch 212 fitted on the spline 211 and operated through a bearing 214 by a clutch operating cylinder 215 to move axially, to the base end of a spindle 217 rotatably fitted to an inner peripheral surface of a spindle head 216 of the turret head 296. A tool holder 220 for holding a slice cutter 219 serving as a tool is held at a leading end of the spindle 217 for rotation in unison with the spindle 217.
The turret head 296 includes another spindle head 221 apart from the spindle head 216, and a spindle 222 having a tool holder 223 held at its fore end is rotatably fitted in the spindle head 221. The individual spindle heads 216 and 221 are formed with their central axes extending at different levels so that the corresponding spindles cannot interfere with each other. During working, the spindle head is in the position 216 shown in solid lines in the drawing and aligned with the spline 211, and in replacing the tool, the turret head 296 is rotated so that the spindle head assumes the position 221 shown by dashed lines.
In the prior art machine tool shown in FIG. 15, the pair of guide rails 291 and 292 constituting a supporting device for the tool-driving unit A' are both disposed on the same vertical plane extending in a lateral direction (i.e., a vertical direction as viewed in FIG. 15) and hence, as compared to the distance from one of the guide rails 291 to the connection of the turret head 296, the distance from the other guide rail 292 to the connection of the turret head 296 is very long, and the amount of overhang from the guide rail 292 on the column 290 is larger. For this reason, the tool-driving unit A' has an unsatisfactory mechanical rigidity, and this is apt to produce vibration and a reduction in horizontal accuracy of the spindle 217 due to machining load during working. In addition, the tool-driving unit A' is subject to thermal variation with respect to the guide rail 292 which adversely affects working accuracy.